Clear m_previousActiveInterpolationsForAnimations in maybeApplyPendingUpdate()

This is a performance-optimization CL for oilpan builds. In oilpan, it is important
to explicitly clear on-heap collections in order not to leave unnecessary garbage
on the oilpan's heap.

BUG=

Review URL: https://codereview.chromium.org/1311683002

git-svn-id: svn://svn.chromium.org/blink/trunk@201053 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/animation/css/CSSAnimations.cpp

@@ -297,10 +297,9 @@ void CSSAnimations::calculateAnimationUpdate(CSSAnimationUpdate& update, const E
 
 void CSSAnimations::maybeApplyPendingUpdate(Element* element)
 {
-    if (m_pendingUpdate.isEmpty()) {
-        m_previousActiveInterpolationsForAnimations.clear();
+    m_previousActiveInterpolationsForAnimations.clear();
+    if (m_pendingUpdate.isEmpty())
         return;
-    }
 
     m_previousActiveInterpolationsForAnimations.swap(m_pendingUpdate.activeInterpolationsForAnimations());